Xen: support maxvcpus in xm and xl config

From: Ian Campbell <ian.campbell@citrix.com>

xend prior to 4.0 understands vcpus as maxvcpus and vcpu_avail
as a bit map of which cpus are online (default is all).

xend from 4.0 onwards understands maxvcpus as maxvcpus and
vcpus as the number which are online (from 0..N-1). The
upstream commit (68a94cf528e6 "xm: Add maxvcpus support")
claims that if maxvcpus is omitted then the old behaviour
(i.e. obeying vcpu_avail) is retained, but AFAICT it was not,
in this case vcpu==maxcpus==online cpus. This is good for us
because handling anything else would be fiddly.

This patch changes parsing of the virDomainDef maxvcpus and vcpus
entries to use the corresponding 'maxvcpus' and 'vcpus' settings
from xm and xl config. It also drops use of the old Xen 3.x
'vcpu_avail' setting.

The change also removes the maxvcpus limit of MAX_VIRT_VCPUS (since
maxvcpus is simply a count, not a bit mask), which is particularly
crucial on ARM where MAX_VIRT_CPUS == 1 (since all guests are
expected to support vcpu placement, and therefore only the boot
vcpu's info lives in the shared info page).

Existing tests adjusted accordingly, and new tests added for the
'maxvcpus' setting.

src/xenconfig/xen_common.c

@@ -488,19 +488,22 @@ xenParseCPUFeatures(virConfPtr conf, virDomainDefPtr def)
     const char *str = NULL;
     int val = 0;
 
-    if (xenConfigGetULong(conf, "vcpus", &count, 1) < 0 ||
-        MAX_VIRT_CPUS < count)
+    if (xenConfigGetULong(conf, "vcpus", &count, 1) < 0)
         return -1;
 
     if (virDomainDefSetVcpusMax(def, count) < 0)
         return -1;
 
-    if (xenConfigGetULong(conf, "vcpu_avail", &count, -1) < 0)
+    if (virDomainDefSetVcpus(def, count) < 0)
         return -1;
 
-    if (virDomainDefSetVcpus(def, MIN(count_one_bits_l(count),
-                                      virDomainDefGetVcpusMax(def))) < 0)
-        return -1;
+    if (virConfGetValue(conf, "maxvcpus")) {
+        if (xenConfigGetULong(conf, "maxvcpus", &count, 0) < 0)
+            return -1;
+
+        if (virDomainDefSetVcpusMax(def, count) < 0)
+            return -1;
+    }
 
     if (xenConfigGetString(conf, "cpus", &str, NULL) < 0)
         return -1;
@@ -1494,14 +1497,10 @@ xenFormatCPUAllocation(virConfPtr conf, virDomainDefPtr def)
     int ret = -1;
     char *cpus = NULL;
 
-    if (xenConfigSetInt(conf, "vcpus", virDomainDefGetVcpusMax(def)) < 0)
+    if (virDomainDefGetVcpus(def) < virDomainDefGetVcpusMax(def) &&
+        xenConfigSetInt(conf, "maxvcpus", virDomainDefGetVcpusMax(def)) < 0)
         goto cleanup;
-
-    /* Computing the vcpu_avail bitmask works because MAX_VIRT_CPUS is
-       either 32, or 64 on a platform where long is big enough.  */
-    if (virDomainDefHasVcpusOffline(def) &&
-        xenConfigSetInt(conf, "vcpu_avail",
-                        (1UL << virDomainDefGetVcpus(def)) - 1) < 0)
+    if (xenConfigSetInt(conf, "vcpus", virDomainDefGetVcpus(def)) < 0)
         goto cleanup;
 
     if ((def->cpumask != NULL) &&

tests/xlconfigdata/test-paravirt-maxvcpus.cfg

@@ -0,0 +1,13 @@
+name = "XenGuest1"
+uuid = "45b60f51-88a9-47a8-a3b3-5e66d71b2283"
+maxmem = 512
+memory = 512
+maxvcpus = 8
+vcpus = 4
+localtime = 0
+on_poweroff = "preserve"
+on_reboot = "restart"
+on_crash = "preserve"
+vif = [ "mac=5a:36:0e:be:00:09" ]
+bootloader = "/usr/bin/pygrub"
+disk = [ "/var/lib/xen/images/debian/disk.qcow2,qcow2,xvda,w,backendtype=qdisk" ]

tests/xlconfigdata/test-paravirt-maxvcpus.xml

@@ -0,0 +1,28 @@
+<domain type='xen'>
+  <name>XenGuest1</name>
+  <uuid>45b60f51-88a9-47a8-a3b3-5e66d71b2283</uuid>
+  <memory unit='KiB'>524288</memory>
+  <currentMemory unit='KiB'>524288</currentMemory>
+  <vcpu placement='static' current='4'>8</vcpu>
+  <bootloader>/usr/bin/pygrub</bootloader>
+  <os>
+    <type arch='x86_64' machine='xenpv'>linux</type>
+  </os>
+  <clock offset='utc' adjustment='reset'/>
+  <on_poweroff>preserve</on_poweroff>
+  <on_reboot>restart</on_reboot>
+  <on_crash>preserve</on_crash>
+  <devices>
+    <disk type='file' device='disk'>
+      <driver name='qemu' type='qcow2'/>
+      <source file='/var/lib/xen/images/debian/disk.qcow2'/>
+      <target dev='xvda' bus='xen'/>
+    </disk>
+    <interface type='ethernet'>
+      <mac address='5a:36:0e:be:00:09'/>
+    </interface>
+    <console type='pty'>
+      <target type='xen' port='0'/>
+    </console>
+  </devices>
+</domain>

tests/xlconfigtest.c

@@ -192,6 +192,7 @@ mymain(void)
             ret = -1;                                                   \
     } while (0)
 
+    DO_TEST("paravirt-maxvcpus");
     DO_TEST("new-disk");
     DO_TEST("spice");
     DO_TEST("spice-features");

tests/xmconfigdata/test-paravirt-maxvcpus.cfg

@@ -0,0 +1,13 @@
+name = "XenGuest1"
+uuid = "c7a5fdb0-cdaf-9455-926a-d65c16db1809"
+maxmem = 579
+memory = 394
+maxvcpus = 4
+vcpus = 2
+localtime = 0
+on_poweroff = "destroy"
+on_reboot = "restart"
+on_crash = "restart"
+vif = [ "mac=00:16:3e:66:94:9c,bridge=br0,script=vif-bridge" ]
+bootloader = "/usr/bin/pygrub"
+disk = [ "phy:/dev/HostVG/XenGuest1,xvda,w" ]

tests/xmconfigdata/test-paravirt-maxvcpus.xml

@@ -0,0 +1,31 @@
+<domain type='xen'>
+  <name>XenGuest1</name>
+  <uuid>c7a5fdb0-cdaf-9455-926a-d65c16db1809</uuid>
+  <memory unit='KiB'>592896</memory>
+  <currentMemory unit='KiB'>403456</currentMemory>
+  <vcpu placement='static' current='2'>4</vcpu>
+  <bootloader>/usr/bin/pygrub</bootloader>
+  <os>
+    <type arch='i686' machine='xenpv'>linux</type>
+  </os>
+  <clock offset='utc' adjustment='reset'/>
+  <on_poweroff>destroy</on_poweroff>
+  <on_reboot>restart</on_reboot>
+  <on_crash>restart</on_crash>
+  <devices>
+    <disk type='block' device='disk'>
+      <driver name='phy'/>
+      <source dev='/dev/HostVG/XenGuest1'/>
+      <target dev='xvda' bus='xen'/>
+    </disk>
+    <interface type='bridge'>
+      <mac address='00:16:3e:66:94:9c'/>
+      <source bridge='br0'/>
+      <script path='vif-bridge'/>
+    </interface>
+    <console type='pty'>
+      <target type='xen' port='0'/>
+    </console>
+    <memballoon model='xen'/>
+  </devices>
+</domain>

tests/xmconfigdata/test-paravirt-vcpu.cfg

@@ -2,8 +2,8 @@ name = "XenGuest1"
 uuid = "c7a5fdb0-cdaf-9455-926a-d65c16db1809"
 maxmem = 579
 memory = 394
-vcpus = 4
-vcpu_avail = 3
+maxvcpus = 4
+vcpus = 2
 localtime = 0
 on_poweroff = "destroy"
 on_reboot = "restart"

tests/xmconfigtest.c

@@ -215,6 +215,7 @@ mymain(void)
     DO_TEST("paravirt-net-e1000");
     DO_TEST("paravirt-net-vifname");
     DO_TEST("paravirt-vcpu");
+    DO_TEST("paravirt-maxvcpus");
     DO_TEST("fullvirt-new-cdrom");
     DO_TEST("fullvirt-utc");
     DO_TEST("fullvirt-localtime");